1. Field of the Invention
The present invention relates generally to data storage systems, and more particularly to network file servers. The present invention specifically relates to a network file server in which file access is shared among a number of processors by granting file locks and distributing file metadata to the processors.
2. Description of the Related Art
Mainframe data processing, and more recently distributed computing, have required increasingly large amounts of data storage. This data storage is most economically provided by an array of low-cost disk drives integrated with a large semiconductor cache memory.
In a network environment, at least one data mover computer is used to interface the cached disk array to the network. The data mover computer performs file locking management and mapping of the network files to logical block addresses of storage in the cached disk array, and moves data between network clients and the storage in the cached disk array.
In relatively large networks, it is desirable to have multiple data mover computers that access one or more cached disk arrays. Each data mover computer provides at least one network port for servicing client requests. Each data mover computer is relatively inexpensive compared to a cached disk array. Therefore, multiple data movers can be added easily until the cached disk array becomes a bottleneck to data access.
Unfortunately, data consistency problems may arise if concurrent client access to a read/write file is permitted through more than one data mover. These data consistency problems can be solved in a number of ways. For example, as described in Vahalia et al., U.S. Pat. No. 5,893,140 issued Apr. 6, 1999, entitled “File Server Having a File System Cache and Protocol for Truly Safe Asynchronous Writes,” incorporated herein by reference, locking information can be stored in the cached disk array, or cached in the data mover computers if a cache coherency scheme is used to maintain consistent locking data in the caches of the data mover computers.
When a large number of clients are concurrently accessing shared read-write files, there may be considerable access delays due to contention for locks not only on the files but also on the file directories. One way of reducing this contention is to assign each file system to only one data mover assigned the task of managing the locks on the files and directories in the file system. This permits the data mover file manager to locally cache and manage the metadata for the files and directories of the file system. For example, as described in Xu et al., U.S. Pat. No. 6,324,581, issued Nov. 27, 2001, incorporated herein by reference, the data mover acting as the manager of a file grants a lock on the file and provides metadata of the file to another data mover servicing a client request for access to the file. Then the data mover servicing the client request uses the metadata to directly access the file data in the cached disk array. Moreover, in some network configurations, the clients can be trusted to access directly the data in the cached disk array. In such a configuration, a network client can send a request for a file lock and file metadata directly to the file manager. Upon being granted a lock on the file and receiving the file metadata, the trusted client can access directly the file data in the cached disk array.